Relationship between static chemical and cyclic mechanical fatigue in a feldspathic porcelain.
OBJECTIVE
The goal of this study was to determine if static chemical and cyclic mechanical fatigue are independent, or if they interact to produce greater than additive strength loss in a feldspathic porcelain.


METHODS
A blunt indentation technique was used to investigate the response of a feldspathic dental porcelain to cyclic mechanical fatigue and static chemical fatigue. All specimens were fabricated in a dry inert environment and then mechanically fatigued by cyclic loading and strength-tested in dry inert nitrogenous, ambient or wet environments. A series of experiments were performed to evaluate the effects of chemical and mechanical fatigue, and their interaction on strength loss; to determine the effects of, and interaction between, the factors of cyclic fatigue environment and strength test environment on strength; to ascertain if the type of environment during strength testing influenced specimen strength; and to distinguish between chemical damage caused by exposure to moisture alone and stress corrosion damage resulting from the strength testing environment, using a pair of two-way analysis of variance, a single one-way analysis of variance and a t-test (p < 0.05).


RESULTS
These experiments indicated that both static chemical fatigue and cyclic mechanical fatigue significantly reduced specimen strength, but they did not interact to produce greater than summative effects. It was also learned that chemical fatigue was not detected on initial exposure to moisture and that it occurred to a small extent during mechanical fatigue cycling, and primarily occurred during strength testing through a stress-corrosion phenomenon. Micrographs visually evaluated the effects of mechanical and chemical fatigue on surface contact damage.


CONCLUSIONS
As both static chemical and cyclic mechanical fatigue influenced porcelain strength, they should both be considered in future evaluations. However, because they largely acted independently, they can be studied separately.
White
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University of Southern California, Los Angeles, USA. shanewhite@juno.com
Li
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ZC
Yu
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Kipnis
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D000538:Aluminum Silicates / Q000737:chemistry*; D000704:Analysis of Variance; D003343:Corrosion; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D019544:Equipment Failure Analysis; D008422:Materials Testing / Q000379:methods; D017680:Potassium Compounds / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry
D000538:Aluminum Silicates; D017680:Potassium Compounds; C110425:Vita VMK 69N; D014867:Water; D003776:Dental Porcelain; C016447:feldspar